Overt activation of monocyte/macrophages (Mphage) and endothelial cells is a common feature of several diseases including sepsis, acute respiratory distress syndrome (ARDS) and atherosclerosis. During the studies in the pathogenesis of leishmaniasis, an intracellular parasitic disease, a major surface molecule of this parasite, namely, lipophosphoglycan (LPG) was found to deactivate Mphage. LPG suppress human Mphage expression of pro-inflammatory cytokine genes and nitric oxide synthase activity but had no effect on control gene in preliminary studies. Furthermore, LPG inhibits gene expression via transcription mechanisms and possibly by inducing a repressor protein(s). Since these factors are required for killing the parasite and T cell-dependent immunity, LPG effectively deactivates Mphage and alters T cell immunity resulting in parasite survival. The findings that LPG suppressed lipopolysaccharide (endotoxin) and cytokine activation of Mphage led to investigations to determine whether this molecule has broader applications. Human vascular endothelial cells are studied because the parasite at cutaneous site of entry traverses vascular endothelium to infect distant Mphage. LPG rapidly binds to endothelial cell and deactivates endothelial cell functions: thrombosis and leukocyte adherence but had no effect on HLA class I expression. Because HIV-1 replication also requires cell activation, we evaluated the effect of LPG on cells chronically infected with HIV. LPG suppressed agonist induction of HIV. The application shows evidence that the inhibitory activity of LPG is not due to low level endotoxin contamination of LPG and excludes a non-specific global effect because neither cell viability nor protein and DNA synthesis were affected by LPG. These findings in murine and human vascular cells suggest that LPG affects fundamental events in cell activation signaling. The application suggests that LPG is a ligand mimetic for undefined host factor(s) and that LPG triggers cell deactivation by utilizing existing host pathways. The mechanisms by which LPG deactivates vascular cells are undefined. It is hypothesized that LPG deactivates vascular cells by binding to membrane receptor(s), triggering specific intracellular and nuclear events, and thus, regulating transcription of multiple genes. The proposed studies will: 1) characterize the biologic effects of LPG on monocytes, 2) determine the specific membrane and intracellular signaling events of LPG, and 3) define the transcription regulation of IL-1B by LPG. Both LPG and endotoxin are evolutionary perfected molecules. LPG deactivates agonist induced cell signaling while endotoxin is a potent inflammatory molecule. By analogy to endotoxin, studies on LPG will identify fundamental mechanisms for vascular cell deactivation and likely have novel applications for several diseases of overt vascular cell activation accounting for a major proportion of acute and chronic illness of American including sepsis, ARDS, disseminated intravascular coagulation, atherosclerosis, autoimmune disease and HIV/AIDS.